1. Field of the Invention
The present invention relates to a fuel cell system using a hydride powder as a source of hydrogen fuel.
2. Discussion of Related Art
A fuel cell is a power generation system that generates electricity by an electrochemical reaction of hydrogen and oxygen. There are several types of fuel cells, each using a different chemistry or electrolyte. Examples of different fuel cells include phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte membrane fuel cells, and alkaline fuel cells, etc. These fuel cells operate on the same general principles, but use different types of fuel, catalysts, electrolytes, and operate at different temperatures, etc. Among the different fuel cells, polymer electrolyte membrane fuel cells (PEMFC) have a high output characteristic and operate at a low operating temperature range. In addition, a PEMFC has rapid starting and response characteristics as compared with other fuel cells. Therefore, PEMFCs can be used in a variety of applications such as transportable power sources for portable electronic equipment, power sources for automobiles, and distributed power sources for stationary power plants for houses and public buildings.
Hydrogen undergoes an electrochemical oxidation reaction at the anode electrode of a fuel cell and has excellent reactivity reacting with oxygen to produce water at the cathode electrode. Such a fuel cell provides an environmental-friendly discharge; hence hydrogen is one of the most suitable fuels for fuel cells. However, pure hydrogen gas is not readily available and hydrogen gas is frequently obtained by reforming hydrogen-rich raw materials.
Fuel cell systems using hydrides which can be stored in a powder form such as NaBH4, etc. have been proposed as a fuel. Such fuel cell systems have high volume storage efficiency. Hydrides can be supplied to a fuel cell in a liquid form or can be used to generate hydrogen in a gaseous form that is supplied to the fuel cell. In the gaseous form, hydrogen gas is first separated from the hydrides through a chemical reaction, and then it is fed to an anode electrode of a PEMFC stack.
Hydrides are compounds that produces hydrogen and heat upon reacting with water. Several examples of hydrides that can be used as a fuel for fuel cells include, but are not limited to, sodium borohydride (NaBH4), lithium borohydride (LiBH4), lithium hydride (LiH), sodium hydride (NaH), and combinations thereof.
There are several ways for supplying hydrides to produce hydrogen to be used as a fuel. When liquid hydrides are used, the size of the fuel cell system increases due to the volume of water. When hydride powder is used, a complex system of delivering and controlling the amount of powder is required. In addition, the reaction time of the hydride powder must be considered in operating the fuel cell.